Hydraulic in-feeding mechanism for diamond tools



Dec. 2, 1958 s. PTBRUCE ETAI. 2,862,492

HYDRAULIG IN-FEEDI'NG MECHANISM FoRfDIAMoND TooLs 2 Sheets-sheet 1` Filed May 27, 1955 Dec. 2, 1958 Ys. P. BRUCE ETAL 2,862,492

'HYDRAULIC IN-FEEDING MECHANISM FOR DIAMOND TooLs 2 Sheets-Sheet 2 Filed May 27, 1955 L tz: [bj-1.5- 'azzfon/P Brace f l. nur '.77 ffbfzzffm Zi Lfhwwwwmfs HYDRAULIC IN-FEEDING MECHANISM FDR Y DIAMOND TOOLSk Stanford P. Bruce yand Arthur T. Kohlstrunk, Detroit, Mich., assgnors to VWheel Trueing Tool Company, Detroit, Mich., a corporation of Delaware `Application May 127, 1955, Serial No. 511,491 6Claims. (Cl. `125'.11)

The present invention relates toa` hydraulic infeeding mechanism for diamond tools, and more lparticularly relates to a mechanism operable to incrementallyadvance tikdiamond tool for `dressing grinding'wheels and the While it will .be appreciated that embodiments of :the present invention are devices of general utility, the invention is described lhere in conjunction with the advancement of diamond tools incrementally Aforwardly for dressing` grinding wheels as Ianexample wherein an embodiment of this invention may enjoy particularly advantageous utility.

This exemplieduseof the present Vinvention has been chosen since the in-feeding'or incremental .advancing of a dressing toolsuch as a diamond dressing tool on ygrinding mechanisms such as centerless grindersy or the like -for dressing the grindingwheels has `been particularly time-consuming and awkward heretofore. 'Prior to the present invention it was necessary for the operator of the grinding machine to leave his stock loading station at the front of the machine and move to the side ofthe machine or the rear of the machine and then return to his position at the front of the machine at least twice in the normal course kof dressing the grinding wheel between grinding operations. This timefconsuming movement of the operator of the machine was required to ybe made several 'times ysince the operator was required to leave his-stockloading station and moveto .the side or rear of the machine in order to manually vadvance .the ldressing to-ol vand open a iluid coolant valve. Thereafter, the operator was required to turn to the front of his machine in order to actuate the traversingmechanism which set the dresser assembly in operation for the lirst or Vrough pass across the'wheel.

After the first rough pass was completedf'the operator was required to return to the manual advancing mechanism for -the dressing tool in order to slightly fur.- ther advance the dressing tool for the nal dressing cut. Then the operator wasrequired to returnk to lthe front of the machine to reactivate Ythe traversing mechanism.

Finally, the operator had to move away from his stock loading station still a third time to operate the coolant liquid valve. l

This manner of advancing the dressing tool was thus extremely .timerconsuming and therefore expensive. Additionally, since the advancing operation for the diamond tool was carried out manually, in many instances theY tool was advanced by `an incrementV which `was either too great or too small with a resultant effect of either'taking much more material from `the grinding wheel `than was necessary, 'or insutliciently dressing the Wheel. By such a manualoperation, even if the dressing of the grinding wheel was finally eiected properly,it,wasnevertheless a non-uniform dressing operation from one Vdressing of the wheel tothe next dressing of the wheel.

By vthe principles of the present invention, however,

the entire dressing operation may be accomplishedwithout any requirement on the part of the operator of-the ICC vdressing tool, yindexing-of the dressing tool, and traversal of the grinding wheel vby the, dressing tool together with initiation and stoppage' of the flow of liquid coolant.y Also, by this'invention there is vprovideda new-and improved mechanism operable by hydraulic 'actuation to incrementvally advance or in-feed the dressingtool whichm'ay be a diamond tool. I v An embodiment of `this invention such asis illustrated inthe drawings includes a lead screw whichzis "coupled to the dressing tool through an indexing mechanism'for incrementally rotating the tool to keep the head lthereof sharp. This lead screw when incrementally rotated -will incrementally advance the tool, and for -thisvpurpose, the lead screw is coupled to a. one-way lor .overrunning clutch `which lis in -t-urn oscillatably driven :by a gear icoupled'to a rack or worm on the piston rod of a piston' and cylinder assembly operable tol beihydr'aulica'lly actua-ted. In vthis 'mechanism actuation of vthe piston "ndcylinder `assembly 4will drive the piston -whichin'turn -willdrive the gear or gear segment and the gear 'or gear segment will in turn drive the one-way Vclutch to drive -the 'screw and thereby incrementally advance the dressing -tool or in-feed the 'dressing tool. p

The advancement of the tool is contolledby lcon- -trolled and varied setting of the -pisto-n whereby the tool infee'd assembly maybe adjustedfor smallincremental in-feed'ing of the toolvv or for large steps of incremental Vadvancement of the tool. i

- To control the step-by-step operation of the inlfeeder,

trollable from any remote position such asthe stock `loading 'station-of the operator'of the grinding machine, and will be described in detail hereinbelow.l

Accordingly, it -is an importantifobjectandffeature of the present invention to provide a -new and improve'dfmechanism -for incrementally advancing a member to be'incrementally advanced.

lStill another object of the present invention is *to provide a new and improved in-feeding mechanism for a dressing tool or the like. v

Still another object of the present invention yis to prov-idel-a-new'and improved in-feeding mechanism whichis hydraulically or otherwise fluid-actuatable for controlled incremental advancement of a member to be so advanced.

Yet 4another object of the present inventionis toprovide a new and improved in-'feeding ymechanism wherein a iluid V-actuatable piston-cylinder fassembly (is coupled through a gearY segment and an overrunning clutch mechanism to a screw shaft for incrementally rotating the'shaft and thereby incrementally advancing a tool. u

Still another object and feature of the present invention is to'pr'ovide a new and improved in-fe'veding mechanism which -is adjustable to variably control the increment of in-feeding'accomplished thereby in each operation'of the in-feeder. Y

Still another object of the present invention is to provide a vnew and limproved control system for a dressing mechanismoperable tol effect controlled traversal of the grindingwheel to be dressed, indexed incremental rotation of the tool, .and Vincremental Aadvancement: of the dressing tool.

Still another object of the present invention is to provide a new and improved control system operable to remotely control several phases of an operation of the `character described.

Still other objects, features and advantages of the present invention will become readily apparent to those skilled in the art and others, from the following detailed description of the present invention and an embodiment thereof, from the claims, and from the accompanying drawings in which each and every detail shown is fully and completely disclosed as a part of this specification, in which like reference numerals refer to like parts, and in which:

Figure 1 is an elevational partly sectioned and partly broken illustration of an in-feeding mechanism embodying the principles of the present invention andshown with the front cover and dial removed-therefrom to better illustrate certain other features of the invention;

Figure 2 is a sectional view of the device of Figure 1 geared substantially along the section line II-II v of Figure 1;

Figure 3 is a schematic illustration of a control system embodying the principles of this invention illustrating the same in an actuating condition for traversal in one direction;

Figure 4 is a schematic illustration of a control system in a neutralized condition; and

Figure 5 is a schematic illustration of a control system shown for traversal in a direction opposite to that shown in Figure 3.

As shown on the drawings:

In Figures 1 and 2, there is illustrated an in-feeding mechanism embodying the principles of the present invention and operable to be mounted on a grinding machine such as centerless grinder at the rear of the machine for advancing a tool such as the tool having a cutting or dressing head such as a diamond 11 thereon toward a grinding wheel 12 which is fragmentally illustrated in Figure 2. The in-feeding mechanism is effective upon actuation thereof to incrementally advance the dressing tool and its head whereby when the dressing tool is trans- .versely moved across the grinding wheel the face of the grinding wheel will be dressed and cut inraccordance with the contour of a cam bar which is engagedby a follower forming a part of the complete mechanism. lSince the cam bar and the follower of the mechanism form no part of the present invention they have not been illustrated here.

To provide for the advancement of the tool 10, the tool is mounted in a tool holder 13 of an indexing mechanism 14 which is operable to incrementally rotate the tool before each traversal of the grinding wheel and is actuatable hydraulically, and the tool indexer 14 is mounted on the dresser barrel 15 which also carries a driving nut 16 threadably engaging a lead screw or screw shaft 17. With this arrangement, incremental rotation of the screw shaft or lead screw 17 will beV effective to incrementally advance or retract the tool 10. Under normal operating conditions of the in-feeder, the lead screwV 17 will be accurately incrementally rotated to advance the tool 10 by accurate stepped increments.

The lead screw shaft 17 is journalled in a bearing 18 which is fixed in an annular stop block 19 fixed in an aperture 20 in a rear plate or back plate 21 of a housing 22 for the in-feeder mechanism. This stop block 19 is also provided with a threaded coupling passage 23 providing for connections. to coolant supply conduits and communicating with a coolant Vtube 24 leading through the dresser barrel to a nozzle 25 for playing a stream of coolant upon the tool head 11 and grinding wheel 12 during the dressing operation.

At the front end of the lead screw shaft, it is provided with a slightly reduced diameter portion 26- which carries a shaft cylinder 27 that is secured thereto by a taper pin or the like 28 for corotation therewith. The inner face 29 of the shaft cylinder 27 closely abuts the front face of the stop block 19 and thus holds the lead screw shaft against axial movement rearwardly when the screw shaft is rotated in a direction to cause the tool 10 to be retracted. Retaining the lead screw Vagainst axial movement forwardly is accomplished by cooperation of'a oneway or overrunning clutch mechanism 30, a clutch ring 31 mounted on the outer peripheral surface of the `shaft cylinder 27,' and a clutch release ring 32 operably disposed against the inner face of a front cover plate 33 on the housing 22 and forming a complete housing together with the back plate 21 and a side plate assembly 34.

Of greater significance, however, in the operational characteristics of the overrunning clutch 30, is that it is so operably assembled together with the shaft cylinder 27, that is is effective to drive the shaft cylinder 27 in only one direction when it is drivingly actuated and to slip on the shaft cylinder when actuated in an opposite direction whereby the shaft cylinder 27 will be incrementally advanced in one angular direction when the one-way clutch 30 is oscillated angularly. To this end, the one-way clutch mechanism 30 includes a clutch ring 31 xed to a clutch race 35 on the outer periphery `of the shaft cylinder 27. On the inner periphery of the clutch race 35 it is provided with a plurality of recesses 36 (Figure 1) which receive rollers 37. The recesses 36 and rollers 37 are so dimensioned that at the angular center of the recesses 36V they have a depth from theouter periphery of the shaft cylinder 27 which is less than the diameter of the roller 37 while the angular ends of the recesses 36 have Va dimension greater than the diameter of the roller 37. The rollers 37 are normally positioned at the counterclockwise extremity of the recesses 36 while springs 38 set in extension recesses 39 in the race 35 normally bias the rollers 37 in a clockwise direction or toward the smaller dimensioned center space (note Figure 1).

With the spacing limited as described, and the springs 38 normally biasing the rollers 37 toward the smaller dimensioned area, any counter-clockwise rotation of the race 35, as the mechanism is Viewed in Figure l, will lock Vthe race 35 to the shaft cylinder 27 through the rollers 37 so that the counter-clockwise rotation of the clutch race 35 will be imparted to the shaft cylinder 27 to counterclockwise rotate the shaft cylinder and thereby counterclockwise rotate the lead screw shaft 17 to advance the tool 10. Clockwise rotation of the clutch race 35 will result in a relative movement thereof with respect to the rollers whereby the rollers will move to their counterclockwise position in the grooves 36 thereby unlocking the race with respect to the shaft cylinder 27 so that the race 35 may be rotated in a counter-clockwise direction without imparting any movement to the lead screw shaft or shaft cylinder. Thus, if the clutch race 35 is oscillated rotationally, the lead screw shaft wil be incrementally rotated and the tool 10 will be incrementally advanced.

To effect this desired oscillation of the clutch race 35, a worm gear or worm gear segment 40 is secured to the clutch ring 31 and to the clutch race 35 by any convenient means such as screws 41 (Figure 1) and the teeth 42 of the gear 40 are drivingly engaged bya worm 4 3 on the outer end of a piston rod 44 which is connected to a piston 45 reciprocably disposed in an actuating cylinder 46 of a piston and cylinder assembly 47. Actuation of the piston and cylinder assembly causes the piston 45 to drive the piston rod 44 and worm 43 which in turn drives the gear segment 40 drivingl'y secured to the clutch race 35 which is thereby incrementally'angularly driven in a counter-clockwise direction as viewed in Figure 1. Upon return of the piston 45 to a deactuated position in the piston and cylinder assembly 47, the clutch race 35 will be returned in a clockwise direction without effecting any movement of the lead screw shaft 17 as described above.

As shown, the piston and cylinder assembly 47 has a single fluid entrance provided at 48 whereby iluid admitted thereto through the entrance A8 will drive the 'piston-i5 downwardly/within the cylinder46. Upongrelief of the pressure ofv the VVfluid in the cylinder 46, the piston 45 w'ill be returned by'action of a spring-49 acting against 'the underside of the piston 45, as at 5E), and bott-oming in 1a -recess 51 in a cylinder cap 52 which is secured tothe back plate 21 of the housing along with the cylinder head l53 which is also secured to the back plate 21 of the housing toffir'mly .and securely mount the piston and cylinder yassembly 47 withinthe housing and forming a part Aof v'the mechanism of this invention.

`In this embodiment of the present invention, the incremental rotation of the gear 40 and therebythe incremental advancement of the tool 10 is readily adjustable `since the stop block 1'9is'provided with a pair of stop `faces 53 land 54 whichaare respectively 'engageable with theclockwise end face S5 and the counter-clockwise end `faee'56 of the quadrant gear segment 40. These stop faces-'S'.ifand 54 in the-stop block 19 are provided `as the ends of a gear-accommodating recess 57 (Figure 2) on the inner'end of the stop block v19 in the second and third yquadrants thereof as viewed in Figure 1. Thus,

with the end face -55 in engagement with the stop face rotation of the gear segment 40 and the clutch race 35 Yis limited. While in such 'a limited return position, the `axial` position ofthe Worm 43 xed o n the piston rod 44 by a pin orset screw y58 may be adjusted by proper rota- 'tion 'of the worm, and piston `rod 'whereby threading engagement'of the worm 43 with the teeth '42 will'vary the 'position vof the worm 43 to move the same axiallyv upwardly Yto increase the stroke length of the piston 454 within the cylinder 46 or axially downwardly to decrease the' stroke length of the piston 4S within the cylinder 46. This rotational adjusting movement of the Worm 43 and piston 'rod44 is facilitated by a screw driver slot 59 in the Youter end of the worm 43 and piston rod 44. When-the worm and rod .are adjusted to an axial upward position, the stroke length of the piston in the piston and cylinder assembly will be increasedwhereby incremental rotation and oscillation o f the gear segment 40 will be 'increased to a greater arc length whereby the lead screw 17 will be incrementally rotated through increments of greater-arclength andthe tool will beradvanced by greater increments to take deeper dressing cuts in the 'grinding wheel 12. vIt follows, of -course, that adjustment ofthe lpiston rod and'worm downwardly to a positionsuch as theposition shown will allow only a very Vshort stroke length of the piston'and thereby allow only a very small incremental advancement of the tool 10.

`When dressingV of a grinding wheel has been completed through asuicient number of operations that it is de- `sirab'le` to replace the grinding wheel, or for someother reason it is found desirable to retract the dressing tool, retraction of the dressing tool may be easily accomplished in .accordance with this invention by application of an axially upwardly directed force to a clutch release rod 60 which is pinned to the'clutch release ring 32 to lrotate the clutch release ring 32 slightly counterclockwise, therod 60 being'pinned to the ring 32 by a pin 61. The clutch release ring 32 carries a pair of axially projectingpins 62 which project into the slots 36 behind the rollers 37 so that when the ring 32 is rotated counter-.clockwise by manipulation of the rod 60, the pins 62y will hold the rollers 37 in their counter-clockwisemost position against the force -of ,springs 38 so that there'will .be rio locking action between the clutch race 35 and the shaft cylinder-27. This enables the `operator to manually rotate the shaft cylinder 27 Yin either direction, and particularly clockwise as viewed -in Figure l to retract the the tool 10.

Similarly, when desirable, in-feeding of the tool 10 may be accomplished manually and to this end `as Well as to provide an aid in the adjustment of the increment of automatic in-feeding by adjusting the axial position of Y53 of fthe stop block 19, as shown in Figure 1,'clockwise rough cut or a rst passcut'on the worm 43, the mechanism is providedlwith an indexed dial 63 secured on a dial insert 64 on the kouter periphery of the shaft cylinder 27 externally of the'front plate '33. The dial insert 64 is tightly fitted onto the outer periphery of the shaft cylinder 27 and the dial 63 is secured thereover and secured in place by a set screw 65 or the like. The outer edge face 66 of the dial 63 is indicia marked for reading from a pointer 67 on thel outer faceof the front cover'plate 33 so that any Vrotationofv the dial 63 either automatically by operation of the hydraulic system hereinafter described, or other operation o f the in-feeder, or manual rotation of the shaft cylinder'as hereinabove described through manipulation of the handle bar 68 projecting through a diametric aperture in the shaft cylinder 27 and fixed in place by a set screw 69 or the like, will readily be indicated on the dial 66in cooperation with the po-inter 67 on the cover plate 33.

As set out hereinabove, the present invention contemplates automatic controlV of not only the in-feeder of this invention described above, but also the tool rotary indexing mechanism 14 and the traversing mechanism, all from the front of the machine at the stock loading station so that the operator need not leave the stock loading station in order to dress the grinding Wheel 12. For this purpose, the present invention contemplates a new and irnproved hydraulic system which is illustrated schematically in Figures 3, 4 and 5 which respectively show taking a the grinding wheel, a neutral position for the system, and taking Y a second dressing cut or second pass across the grinding wheel. Referring "first to Figure Y4, which shows the hydraulic 'system in its neutral position, the system utilizes the hydraulic pump 70 on the grinding machine for pumping oil from a reservoir 71'and pumping thel same to feed fluid into the system and particularly to a four-way selector valve 72 through a hydraulic feedtube or pipe 73. When the system is in a neutral position, the pump will be by-passed by the selector switch valve to return the fluid pumped from the supply reservoir or tank 71 back to the tank 71. It should be noted that for convenience in the schematic illustrations of Figures 3, 4 and 5, the reservoir 71 has been illustrated in three individual sections forconvenience, it being understood, of course, that the reservoir 71 maybe anytypetof desired'uidfreservoir operable in this system. l W Y 'While the hydraulic system Aisin a neutral position, the pump 70will also supply lluid under pressure to a lfeed pipe or tube 74 which leads to one passage terminal 75 of la pilot sequence valve 76 lwhichis illustrated structurally in Figure l. This time, however, the passage is closed by the pilot valve piston 77'which is in its deactuated position and held in such'position bya biasing member 78 (Figure 4*). Also at this time, both'the piston and cylinder assembly 47 of the infeed mechanism and the tool rotary indexing mechanism 14 are hydraulically deactuated and hydraulic duid may be drained therefrom through a fluid passage tube or pipe 79 leading to a second passage 80 in the pilot `sequence valve 76, and this second passage 80 is in communication with a third passage 81 which is connected with a fluid tube V82 leading to an inlet to the pilot valve, portion 83 of'a ballcheck pilot valve 34, the inlet 85 being in communication with an outlet 86 leading back tothe reservoir 71.

i In the ball-check pilot valve V83 the Valve piston 87 is Cri also in its neutral deactuated position and is so held by biasing means 8S so as to permit communication between the passages 85 and 86.

To incrementally advance la tool by actuation of the vin-feeder mechanism, rotationally,incrementally index the tool and then traverse theV grinding wheel with the tool, the selector valve, which maybe positioned at Lthefront .of the machine adjacent to the stock loading stationyiis Y moved to the rposition shown therefor inFigure -3. J-In such'a position, huid. is supplied `from Vthe pump'i .47 and the rotary indexer 14.

7 through the selector valve 72 Vand into the passage tube 89 leading to the right side of the ball portion 99 of the ball-check pilot valve 84 and to the rod end 91 of the dresser traveler cylinder and piston assembly 92. Admission of pressurized fluid into the ball-check pilot valve causes a depression of the valve piston 87 and actuation thereof whereby the outlet passage 86 is closed and the inlet passage 85 is open to receive uid from the ballcheck chamber 93 and pass the same to the tube S2 to supply fluid under pressure to the top of the valve piston 77 of the pilot sequence Valve 76 whereby the pilot sequence valve is actuated. Then, with the pilot sequence valve actuated the pump 70 will supply pressurized hydraulic fluid through the passages 74 into the first inlet 75 of the valve 76, the pressurized uid then passing7 through the second passage 80 to the flow tube 79 for actuation of both the in-feed piston and cylinder assembly By this sequence of events, the in-feed cylinder and rotary indexing mechanism are both actuated prior to engagement of the dressing tool with the wheel 12 as the dressing tool is traversely moved by its coupling with the piston 94 of the dresser transverse piston and cylinder assembly 92. It is noted here that the iluid in the cap end 95 of the dresser traveler cylinder and piston assembly 92 is exhausted through a fluid tube 96 leading to the selector valve and therethrough back to the reservoir 71. The tube 96 also serves at this time to exhaust the closed side of the ball-check chamber 93 of the ball-check pilot valve through a ow tube 97.

At the conclusion of the rst pass, the selector valve may be returned to its neutral position whereby the valves yare deactuated and the in-feed mechanism and rotary indexing mechanism are also deactuated as evidenced by the hydraulic circuitry of Figure 4.

The second pass of the dressing tool over the grinding wheel and further indexing of the tool and in-feeding thereof is accomplished by moving the selector valve to the position shown therefor in Figure 5. When the selector valve is in the position of Figure 5, pressurized lluid will be supplied to the left side of the ball-check chamber 93 through the tubes 96 and 97, the tube 96 also supplying pressurized fluid to the cap end 95 of the dresser traveler cylinder and piston assembly 92. Fluid supplied to the ball-check pilot valve 84 will so actuate `the piston 37 thereof as to admit fluid through the passage 85 to the pilot sequence valve 76 to actuate the piston'77 thereof whereby the pilot sequence valve will permit the passage of nid from the pump 70 to the in-feed cylinder and piston assembly 47 and to the indexing mechanism 14 for in-feeding the tool and rotationally indexing the same.

Thus, the tool 10 will be in-fed and indexed before the traversing mechanism causes the same to engage the grinding wheel 12. The traversing mechanism will, of course, be actuated through supply of pressure fluid to the cap end 95 thereof while the rod end 91 thereof is exhausted through the passage tube 89 which leads through the selector valve 72 back to the reservoir 71.

From the foregoing it will be readily observed that by the principles of the present invention there is provided a wholly new and improved in-feed mechanism and control system for dressing grinding wheels and the like and that numerous variations and modifications may be elfected without departing from the true spirit and scope of the novel concepts and principles of this invention. We, therefore, intend to cover all such modifications and variations as fall within the true spirit and scope of the novel concepts and principles of this invention.

We claim as our invention:

1. In a mechanism for dressing a grinding wheel by traversing the wheel with a dressing tool, means to incrementally advance the dressing tool comprising a housing, a screw shaft journalled in said housing and coupled to said dressing toolV whereby incremental rotation of the screw shaft incrementally advances the dressing tool, Va one-way drive overrunning clutch coupled to said screw shaft within said housing to rotate the screw 'shaft when driven in one direction and to slip on the screw shaft when driven in an opposite direction, a worm gear secured to said clutch to drive the same, a worm `in driving engagement with said worm gear to drive the worm gear by axial movement of the worm, and a piston and cylinder assembly mounted in said housing with the piston connected to said worm whereby said worm is axially moved upon actuation of the piston and cylinder assembly to displace the piston therein.

2. In a mechanism for dressing a grinding wheel by traversing the wheel with a dressing tool, means to advance thedressing tool an adjustable incremental distance comprising, a housing, a screw shaft journalled in the housing and coupled to said dressing tool whereby incremental rotation of the screw shaft incrementally advances the dressing tool, a one-way drive overrunning clutch coupled to said screw shaft within said housing to rotate the screw shaft when driven in one direction and to slip on the screw shaft when driven in an opposite direction, drive means coupled to said one-way clutch to oscillatably actuate the same, means adjusting the amount of movement of said drive means to thereby vary the increments of said incremental distance and means to release the overrunning clutch from the screw shaft whereby the screw shaft is rotatably operable independentof the drive and overrunning clutch.

3. -In a mechanism for dressing a grinding wheel wherein the wheel is traversed by a dressing tool, means to incrementally rotatably index the dressing tool, means to traverse the grinding wheel with the dressing tool, and means to incrementally advance the `dressing tool an adjustable incremental distance, and a remotely controllable hydraulic actuating system operable to effect actuation of said means to by-directionally traverse the grinding wheel with said tool and to index the tool and simultaneously incrementally advance the tool prior to engagement of the tool with the grinding wheel upon traversal of the grinding wheel by the tool in each direction.

4. In a mechanism for dressing a grinding wheel wherein the wheel is traversed by a dressing tool, means to drive the tool to traverse the grinding wheel, means to rotatably index the tool, and means to incrementally advance the tool, and a hydraulic system coupled to all of said -means and including a ball-check pilot valve controllably actuating a pilot sequence valve permitting pressurized Huid to flow to the rotatable indexing means and the incremental advancing'means whereby the tool is advanced and indexed before the tool engages the grinding wheel in traversing movement.

5. An incremental advancing mechanism comprising a housing, a lead screw shaft journalled in said housing, an overrunning clutch coupled to said screw shaft, a stop block in said housing, a gear segment secured to said clutch mechanism and oscillatable between positions of engagement with said stop block, comprising a reciprocable member connected to said gear segment, and means for adjusting the stroke of reciprocation of the reciprocable member to vary the increment of movement of said screw shaft upon reciprocation of said reciprocable member means to oscillatably drive said gear segment.

6. An incremental advancing mechanism comprising a housing, a screw shaft journalled in said housing, an overrunning clutch coupled to said screw shaft, a gear secured to the overrunning clutch, a worm in driving connection with said gear, piston and cylinder means connected to said worm to oscillatably drive the gear and clutch, and means to adjust the position of the worm on the gear whereby the arc length of oscillation is variably controllable.

(References on vfollowing page) References Cited in the le of this patent UNITED STATES PATENTS Wilcox Aug. 25, 1925 Bath July 25, 1933 5 Wilneland Sept. 12, 1933 Asbridge Haas Sept. 26, 1933 Oct. 9, 1934 1o A Romaine Apr. 9, 1935 Crowdson Dec. 7, 1937 Martin Sept. 12, 1950 Silven Sept. 12, 1950 Payne Apr. 21, 1953 Haas June 16, 1953 Hill Aug. 11, 1953 

